Internet usage is increasingly expanding, resulting to the growth of business offering Internet access to various customers. These Internet Service Providers (ISPs) are confronted with a new competitive landscape, which is characterized by a significant complexity and dynamics. This situation justifies a need for measuring customer satisfaction and analyzing factors that are able to affect customer retention. Furthermore, in order to face increasing competition, the ISPs try to fulfill individual customer expectations by diversify their service packages. This paper refers to a customer satisfaction survey for a major ISP in Greece. The analysis is based on the MUSA method, which is an ordinal regression model based on the principles of multicriteria decision analysis. The provided results are able to evaluate quantitative global and partial satisfaction levels and to determine the strong and the weak points of the ISP. Moreover, segmentation analysis is performed in order to identify the different groups of customers and estimate the homogeneity of preferences in distinguished customer segments. All these results are able to help business organization to determine specific improvement actions and develop customized services.